1. Field of the Invention
The present invention relates generally to integrated circuit chip package technology and, more particularly, to a semiconductor package including stacked semiconductor dies which are separated from each other by an adhesive layer alone or in combination with an insulative layer, the semiconductor dies being electrically connected to an underlying substrate through the use of conductive wires, some of which may be fully or partially encapsulated by the adhesive layer.
2. Description of the Related Art
Semiconductor dies are conventionally enclosed in plastic packages that provide protection from hostile environments and enable electrical interconnection between the semiconductor die and an underlying substrate such as a printed circuit board (PCB) or motherboard. The elements of such a package include a metal leadframe, an integrated circuit or semiconductor die, bonding material to attach the semiconductor die to the leadframe, bond wires which electrically connect pads on the semiconductor die to individual leads of the leadframe, and a hard plastic encapsulant material which covers the other components and forms the exterior of the semiconductor package commonly referred to as the package body.
The leadframe is the central supporting structure of such a package, and is typically fabricated by chemically etching or mechanically stamping a metal strip. A portion of the leadframe is internal to the package, i.e., completely surrounded by the plastic encapsulant or package body. Portions of the leads of the leadframe extend externally from the package body or are partially exposed therein for use in electrically connecting the package to another component. In certain semiconductor packages, a portion of the die attach pad or die pad of the leadframe also remains exposed within the package body. In other semiconductor packages, the metal leadframe is substituted with a laminate substrate to which the semiconductor die is mounted and which includes pads or terminals for mimicking the functionality of the leads and establishing electrical communication with another device.
Once the semiconductor dies have been produced and encapsulated in the semiconductor packages described above, they may be used in a wide variety of electronic devices. The variety of electronic devices utilizing semiconductor packages has grown dramatically in recent years. These devices include cellular phones, portable computers, etc. Each of these devices typically includes a printed circuit board on which a significant number of such semiconductor packages are secured to provide multiple electronic functions. These electronic devices are typically manufactured in reduced sizes and at reduced costs, which results in increased consumer demand. Accordingly, not only are semiconductor dies highly integrated, but also semiconductor packages are highly miniaturized with an increased level of package mounting density.
In currently known semiconductor packages, the electrical connection of the semiconductor die to the leadframe or the underlying substrate is most typically accomplished through the use of electrically conductive wires. As indicated above, these conductive wires are used to electrically connect pads on the semiconductor die to individual leads of the leadframe or the pads or terminals of the substrate. These conductive wires are usually made of gold due to its excellent reliability and electrical conductivity. As also indicated above, these conductive wires are typically covered by the hard plastic encapsulant material which ultimately forms the package body of the semiconductor package. This encapsulant material is often an epoxy molding compound (EMC) which itself has excellent thermal property, electrical property, and a high level of formability, thus making such material well suited to protecting the semiconductor die and the conductive wires.
In addition to the foregoing, even though semiconductor packages have been miniaturized, space on a printed circuit board remains limited and precious. Thus, there is an ongoing need to find semiconductor package designs which maximize the number of semiconductor packages that may be integrated into an electronic device, yet minimize the space needed to accommodate these semiconductor packages. One method to minimize space needed to accommodate the semiconductor packages is to stack the semiconductor packages, individual semiconductor dies, or other devices on top of each other, or to stack the semiconductor dies or other devices within the package body of a semiconductor package. However, in those semiconductor packages including stacked semiconductor dies, there is typically a need to interpose an insulative film between the semiconductor dies to prevent current leakage flow. However, in known stacked die semiconductor package designs, the integration of the insulative film into the semiconductor package often gives rise to difficulties in controlling the thickness thereof. Additionally, stresses and delaminations are sometimes caused due to the differences in the thermal expansion coefficients between the insulative film and those materials to which it is attached within the semiconductor package. Further, in known semiconductor package designs wherein an adhesive film, alone or in combination with an insulative film, is interposed between the stacked dies, manufacturing difficulties are often encountered in stacking a top die on a bottom die when the size of the top die exceeds that of the bottom die. Such manufacturing difficulties include the slow production rates and high production costs attributable to the obstacles which typically arise in attempting to ensure that the encapsulant material used to form the package body of the semiconductor package adequately flows between the top and bottom dies. Therefore, a new solution is needed, such solution being provided by the present invention which is discussed in detail below.